1. Technical Field
The present invention relates to a hybrid construction machine.
2. Related Art
Conventionally, a hybrid construction machine is known provided with an engine that generates motive power, a generator-motor that assists the engine, and an electric storage device connected to the generator-motor. The electric storage device includes a battery having an internal resistance which becomes larger in a low-temperature state compared to a normal-temperature state to thereby make the charging and discharging performance of the electric storage device consequently decline. Specifically, when the electric storage device is in a low-temperature state, the discharge current falls compared to a normal-temperature state, thus making it necessary to raise the charging voltage.
Under the circumstances, Japanese Patent Application Publication No. 2010-127271 discloses a method for warming an electric storage device. This method includes operating the generator-motor to charge and discharge the electric storage device when the temperature of the electric storage device is lower than a predetermined temperature, thereby causing the electric storage device to generate heat.
This method, however, involves the operation of the generator-motor as an electric motor according to the discharge from the electric storage device for warm-up, which may cause an excess of the assist power which the generator-motor outputs, that is, the power for assisting the engine. The excess assist power may excessively increase the rotational speed of a hydraulic pump connected to the engine and the generator-motor, for example, to a level exceeding the permitted speed, thus generating possibility of faults in the hydraulic pump or loss of life of the engine.